Try this option:
According to property such triangle
1. area=0.5*a*b, where a and b - the sides of angle 90°.
Using this equation: 180=0.5*40*b, ⇒ b=9.
2. c²=a²+b², ⇒c=√(9²+40²)=41 - the third side of the triangle;
3. Perimeter=a+b+c=9+40+41=90 cm.
answer: 90 cm.
